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All of this effort to create a solid model isn’t just to create a pretty picture. Once your model is drawn and built, you can obtain information about its physical properties. In this section, you will look at a few of the commands that let you gather such information.

Finding a Model’s Mass Properties

You can find the volume, the moment of inertia, and other physical properties of your model by using the Massprop command. These properties can also be recorded as a file on disk so you can modify your model without worrying about losing track of its original properties.

1. Open the Bracket drawing you worked on through most of this chapter.
2. Click and drag the Distance tool on the Standard toolbar. Select Mass Properties on the flyout, or enter Massprop↵.
3. At the Se1ect obj ects: prompt, select the two halves of the solid model. AutoCAD will calculate for a moment, and then it displays a list of the object’s properties.

Taking Advantage of Stereolithography

A discussion of solid modeling wouldn’t be complete without mentioning stereolithography. This is one of the more interesting technological wonders that has appeared as a by-product of 3D computer modeling. Stereolithography is a process that-generates resin reproductions of 3D computer solid models. It offers the mechanical designer a method of rapidly proto typing designs directly from AutoCAD drawings. The process requires special equipment that will read computer files in a particular format.

AutoCAD supports stereolithography through the Stlout command. This command generates an .stl file, which can be used with Stereolithograph Apparatus (STA) to generate a model. You must first create a 3D solid model in Aut oCAD; then you can proceed with the following steps to create the  file.

1. Choose File >- Export.
2. In the Export Data dialog box, open the Save as Type drop-down list and select Lithography (*.stl).Click the Save button.

The AutoCAD 3D solids are translated into a set of triangular-faceted meshes in the  file. You can use the Facetres system variable to control the fineness of these meshes. See Chapter 17for more information on Facetres.

If You Want to Experimet

This chapter has focused on a mechanical project, but you can, of course, use solids to help simplify the construction of 3D architectural forms. If your interest lies in architecture, try drawing the window. (Imagine trying to create this window without the solid-modeling opabilities of AutoCAD!)

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